1. Field
Embodiments of the present invention relate to a method of swing stopping control and a system of swing stopping control for carrying out swing stopping of a suspended load of a suspension type crane when carrying the suspended load to a target position by a trolley in the suspension type crane that is used for loading and unloading work at sites such as harbors, iron works and various kinds of factories.
2. Description of the Related Art
In loading and unloading work carried out by using a suspension type crane, from the view point of improving the efficiency of the loading and unloading work by reducing cycle time, not only positioning control that makes a suspended load correctly reach a target position in a short time but also swing stopping control is generally required that makes a deviation angle of the rope of the suspended load from the vertical direction reduced to zero when the suspended load is carried to the target position. For actualizing such swing stopping control, various kinds of control methods have been previously proposed.
In Japanese Patent No. 3,019,661 (paragraphs [0011] to [0015] and FIG. 3, FIG. 5, FIG. 7, etc.), for example, a crane operation control method is described in which the acceleration of a trolley is continuously changed to smoothly change the trolley speed. In the method, an acceleration pattern is set into a positive and negative triangle-like or trapezoid-like form with a constant speed section in between, by which a slip caused between a trolley wheel and a rail due to a rapid change in a trolley speed is prevented to make positioning accuracy and swing stopping accuracy of a trolley improved.
Moreover, in JP-A-7-257876 (paragraphs [0009] to [0013] and FIG. 5, etc.), a swing stopping control method is disclosed which is applied in the case in which the length of a rope holding a suspended load up is changed as in the case of carrying out lifting or lowering of the suspended load and traversing a trolley at the same time. Namely, the control method is a method in which the swinging period of a suspended load is obtained on the basis of an equation of motion with respect to a deviation angle of the rope of the suspended load from the vertical direction by using representative values of attenuation coefficients and natural frequencies that vary depending on the length of the rope, and then compensate the acceleration of the trolley at the time being halfway through the swinging period (such as the time at one-half of the period) to thereby produce such a speed pattern as to reduce a residual swing.
In the related art according to Japanese Patent No. 3,019,661, an acceleration pattern of the trolley is formed on the basis of the swinging period of a suspended load obtained with respect to a fixed rope length without assuming the case in which the rope length changes on the way of the traversing of the trolley. Thus, in the case in which a rope length changes, the related art can not be directly applied to the case.
In the related art according to JP-A-7-257876, there was a problem in that such a speed pattern that the speed of a trolley changes in the course of acceleration or deceleration of the trolley is formed to thereby require complicated acceleration correction operations.
Moreover, in the case of generally carrying out swing stopping control with a suspended load likened to a simple pendulum, a reference swinging period that is set beforehand causes the swinging condition of the suspended load to be changed, by which it is difficult to set the swinging period to the optimum value.
Accordingly, it is an object of embodiments of the invention to provide a method of swing stopping control and a system of swing stopping control in each of which a required speed pattern is produced by relatively simple arithmetic operations to permit highly accurate swing stopping of a suspended load even in the case in which the length of a rope holding a suspended load up is changed.
Moreover, it is another object of embodiments of the invention to make it possible to carry out highly accurate positioning of a trolley by carrying out an operation with respect to an adequate deceleration initiation distance of the trolley and initiating the deceleration of the trolley at the time when the positional deviation of the travel of the trolley to the target position of the trolley becomes equal to the deceleration initiation distance obtained from the operation.